What are the causes of respiratory failure?

Every time we take a breath in we are taking oxygen from the air down to the lungs. This crosses over into the blood and is then transported to the various organs. At the same time carbon dioxide, which is the waste gas produced by organs, crosses from the blood and into the lungs - we then breathe this out.

This whole process requires an interplay of various systems such as the lungs, the heart, the chest muscles and the brain. When any of these are impaired we are at risk of respiratory failure. Respiratory failure is defined by low blood oxygen levels and there may also be raised blood carbon dioxide levels.

There are various causes of respiratory failure, the most common being due to the lungs or heart. The lung disorders that lead to respiratory failure include chronic obstructive pulmonary disease (COPD), asthma and pneumonia. Heart disease that can lead to respiratory failure can be heart failure which may or may not be accompanied by a heart attack.

Types of respiratory failure

Respiratory failure can be divided into two types:

Type I respiratory failure - the blood oxygen is low and the carbon dioxide is normal or low.

Type II respiratory failure - the blood oxygen is low and the carbon dioxide is high.

Respiratory failure can also be described according to the time it takes to develop:

Acute - happens within minutes or hours; usually, the patient has no underlying lung disease.

Chronic - occurs over days and usually there is an underlying lung disease.

Acute on chronic - this is usually a sudden or quick worsening of the respiratory function in someone who already has chronic respiratory failure.

Causes of respiratory failure

Common causes of type I respiratory failure

Chronic obstructive pulmonary disease (COPD).

Pneumonia.

Pulmonary oedema.

Pulmonary fibrosis.

Asthma.

Pneumothorax.

Pulmonary embolism.

Pulmonary hypertension.

Cyanotic congenital heart disease.

Bronchiectasis.

Acute respiratory distress syndrome.

Respiratory illness associated with HIV infection.

Kyphoscoliosis.

Obesity.

Common causes of type II respiratory failure

COPD.

Severe asthma.

Drug overdose, poisoning.

Myasthenia gravis.

Polyneuropathy.

Poliomyelitis.

Muscle disorders.

Head injuries and neck injuries.

Obesity.

Pulmonary oedema.

Acute respiratory distress syndrome.

Hypothyroidism.

What are the symptoms of respiratory failure?

It is possible that respiratory failure can occur slowly and that patients adapt, such as walking slower and avoiding physical tasks. This is less common and patients may complain of the following symptoms:

Shortness of breath - at first, this may happen only on exertion; however, later on it may also occur at rest and when trying to sleep.

Tiredness - this is due to a lack of oxygen getting to the body's organs.

A bluish tinge to the hands or lips - the medical term for this is 'cyanosis'. It can be noticed when at rest and may worsen with exertion.

Confusion and reduced consciousness - this can occur when either the blood oxygen levels are low or when the carbon dioxide level increases.

There may also be features of the underlying cause - for example, chest pain in heart disease, weakness of limbs in neurological disorders, wheeze in asthma.

When the healthcare professional makes an assessment, they may find the following:

High breathing (respiratory) rate.

A bluish tinge to lips and fingers (cyanosis).

Restlessness, anxiety, confusion, fits (seizures) or coma - these can occur due to the abnormalities in blood gases.

On listening to the lungs there may be noises suggestive of infection, fluid overload or asthma, depending on the underlying cause.

There may also be features of right-sided heart failure which can occur due to the strain on the heart. This is called 'cor pulmonale' and there will be fluid retention evidenced by an enlarged liver, swelling of the tummy (abdomen) and swelling of the legs.

How is the diagnosis of respiratory failure made?

The diagnosis of respiratory failure requires an arterial blood gas which provides information on the levels of the blood oxygen and carbon dioxide levels. An arterial blood gas simply involves a needle connected to a syringe, which is then inserted at the wrist directly into the point where the pulse can be felt. Sometimes the pulse at the wrist is weakened and so a different site has to be used: this is usually the groin and, less commonly, the elbow.

Finding the underlying cause of respiratory failure

Once the diagnosis has been made, further investigations will be required to find the underlying cause. This may include:

Chest X-ray: this may show infection, fluid or tumours of the lung.

Blood tests: these may include full blood count, kidney tests and liver function tests. They may help to work out the cause and also to detect any factors that may be worsening the respiratory failure, such as a low blood haemoglobin level (anaemia).

Troponin blood tests: these are used to determine if there has been recent heart injury - for example, a heart attack which may have caused the respiratory failure.

Spirometry: this is used to measure the lung volumes and capacity and is useful in the evaluation of chronic cases.

A heart ultrasound scan (echocardiography): this can look for cardiac causes, such as a leaking heart valve or heart failure.

What is the treatment for respiratory failure?

Patients with sudden-onset (acute) respiratory failure or a new diagnosis of chronic respiratory failure need to be admitted to hospital immediately. They need to be resuscitated and may need admission to an intensive care unit or the high dependency unit (based on how unwell the patient is) with artificial ventilation and life support. On the other hand many patients with chronic respiratory failure can be treated at home. This will depend on how severe the respiratory failure is, the underlying cause, whether other illnesses are present and the patient's social circumstances. Some patients may need ventilators at home and oxygen support.

Treatment will aim to improve the blood oxygen levels and remove the waste gas carbon dioxide if it is raised. This will usually require artificial ventilation. Further treatment will be aimed towards the underlying cause, such as antibiotics in pneumonia or diuretics in heart failure.

Treatment will be directed towards correcting the blood oxygen and carbon dioxide levels and treating the underlying cause.

Treatment of respiratory failure

This may include:

Oxygen - high levels will be given through a mask (although lower levels may be needed in patients with chronic respiratory failure who have adapted to high carbon dioxide levels).

Artificial ventilation:

Mechanical ventilation:

This involves the patient being put into a coma, using medication and paralysing their breathing.

A tube is inserted into the trachea and an artificial ventilator then does the work of breathing.

Once the underlying cause is treated, patients will be 'weaned' off the ventilator so that their lungs start to do the work of breathing.

This is a form of 'invasive' ventilation.

Non-invasive ventilation (NIV):

This is an alternative to invasive ventilation and is increasingly being used, especially in cases where weaning from an artificial ventilator may prove difficult.

It is used when there is a low blood oxygen level and high blood carbon dioxide level, ie type II respiratory failure. The main disease it is used in is chronic obstructive pulmonary disease (COPD).

It can also be used to help wean patients from invasive ventilation.

Extracorporeal membrane oxygenation (ECMO):

This is a more recent technique being used in patients of all ages.

It involves blood being artificially removed from the body and then oxygen being added by a machine whilst carbon dioxide is removed. The blood is then returned to the patient.

One of the main uses of this method in adults at present is in severe heart failure where other treatments have failed.

The underlying cause may also require treatment - for example, steroids and antibiotics.

For some patients there may not be any further treatment options and their respiratory failure may be terminal. They may benefit from the palliative care team, which deals with managing patients with terminal illnesses.

What are the complications of respiratory failure?

As a result of respiratory failure various complications can occur, including:

Lung complications: for example, a blood clot on the lung (pulmonary embolism), irreversible scarring of the lungs (pulmonary fibrosis), a collection of air between the lung and chest wall (pneumothorax) which can further compromise breathing, chronic respiratory failure and dependence on a ventilator.

Increase in blood count (called polycythaemia): the increased level of red cells occurs from low blood oxygen levels but can lead to blood clots, due to sluggish flow in the blood vessels.

Neurological complications: a prolonged period of low blood oxygen levels can deprive the brain of oxygen, which may be irreversible and may present as coma, fits (seizures) and even brain death.

Prolonged hospital admissions can lead to the following complications:

Hospital-acquired infections: for example, pneumonia and diarrhoea. A pneumonia is likely to put further strain on the respiratory function and can require a need for further ventilation.

Malnutrition which may require assisted feeding methods, such as a tube being inserted down the nose into the stomach (nasogastric feeding), or providing nutrition through a needle straight into the bloodstream. Both of these methods have complications of their own.

Complications from being bed bound for long periods: wasting of limbs with associated weakness, pressure sores, deep vein thrombosis and mental depression.

What is the outlook following respiratory failure?

How well a patient does depends on several factors, including age, the underlying cause and whether it is treatable, the speed of diagnosis and presence of any other illnesses and complications.

Some patients may become worse despite treatment and they may not survive. If someone can no longer be treated with a view to cure, but still needs symptom control, they may be referred to the palliative care team in hospital or to the Macmillan nurses in the community.

Can respiratory failure be prevented?

Smoking is a key factor in many cases of respiratory failure and stopping smoking and/or never smoking are important to prevent respiratory failure.

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